1. Field of the Invention
The present invention relates to an actuator which is releasably attached to the apparatus which it is intended to operate. The actuator has a particular, but non-limiting, application to valve operation in oil production systems, especially sub-sea systems.
2. Description of the Prior Art
It is known to actuate a valve using a piston reciprocally received in a chamber and acting on the valve stem. Operating fluid is introduced into the chamber in order to drive the piston. In some arrangements operating fluid is present, at various times, on both sides of the piston. The chamber and its associated operating fluid passageways are charged when the actuator is attached to the valve. A seal prevents escape of the fluid between the chamber housing and the valve stem.
There are situations in which it would be advantageous for the actuator to be releasably attached to the valve, but in which charging with operating fluid subsequent to attachment of the actuator is not readily achievable. This problem can be acute in sub-sea applications. As the actuator is immersed, sea water will flood the chamber to one side of the piston, via the stem receiving aperture to the chamber. Moreover, the releasable attachment of the actuator is of little benefit if the attachment involves bolting or screwing of the actuator to the valve--especially in deep water applications where diver access is difficult or impossible.